It is an object of the present invention to provide a hydraulic apparatus which is designed to variably control the discharge from a variable displacement pump by detecting changes in momentum of the flowing fluid, which are proportional to the mass flow rates, so that the rate of discharge from the type of pump will be accurately controlled to a prescribed rate without being influenced by changes in viscosity of the fluid or where cavitation, bubbling, or the like occurs in the flow.
The principle on which this invention is based will now be explained with reference to FIG. 1 hereunder.
The force F which acts on a control surface S can be reduced to a formula EQU F=(momentum of the fluid flowing into the control surface S)-(momentum of the fluid flowing out of the control surface S)
With .theta..sub.1 as the inflow angle which the fluid makes with respect to a certain direction as it flows into the control surface S, .theta..sub.2 as the outflow angle which the fluid makes with respect to said certain direction as it flows out of the control surface, V.sub.1 as the velocity at which the fluid flows into the control surface S, V.sub.2 as the velocity at which the fluid flows out of the control surface S, and Q as the quantity of the fluid which flows into and out of the control surface S, the above-mentioned formula regarding momentums in said certain direction of the control surface S can be developed into an equation: EQU F=.rho..multidot.Q(V.sub.1 cos .theta..sub.1 -V.sub.2 cos .theta..sub.2) +.rho..multidot.L.multidot.Q+F.tau.+.alpha.
wherein
.rho. represents the density of the flowing fluid, PA0 L: a damping length (a component in said certain direction of the distance between the inflow and outflow of the flowing fluid in the control surface), PA0 Q: dQ/dt, PA0 F.tau.: a viscous, frictional force generated between the flowing fluid and the inner surfaces within the control surface as the fluid flows past them, PA0 .alpha.: a transient force required to accelerate an object as a whole when the object, surrounded by the control surface, is moved by a force applied by the flowing fluid.
Since, ordinarily the term (.rho..multidot.L.multidot.Q+F.tau.+.alpha.) represents so small a value as to be negligible as compared with the term .rho..multidot.Q (V.sub.1 cos .theta..sub.1 -V.sub.2 cos .theta..sub.2), the above formula can be reduced to an equation EQU F=.rho..multidot.Q (V.sub.1 cos .theta..sub.1 -V.sub.2 cos .theta..sub.2)(1)
With A.sub.1 as the cross-sectional area of the inflow opening for leading the fluid into said control surface S and A.sub.2 as the cross-sectional area of the outflow opening for leading the fluid out of the control surface S, and considering V.sub.1 =Q/A.sub.1 and V.sub.2 =-Q/A.sub.2, the equation (1) can be developed into an equation ##EQU1## which, considering .theta..sub.1 =.theta..sub.2 =.theta. and A.sub.1 =A.sub.2 =A, can further be developed into an equation ##EQU2## Accordingly, the mass flow rate (.rho..multidot.Q) can be represented as a function of the force in a certain direction with .theta., A and p as constants, so that a mass flow rate can be determined by measuring the force F which represents the flow rate.
As illustrated in FIG. 2, a hydraulic apparatus according to the present invention is composed of a variable displacement pump 571, a flow detective unit 501 and a means for setting a mass flow rate 561; said variable displacement pump 571 has a discharge control unit 572 for variably controlling the discharge rate by pressure of fluid; said flow detective unit 501 comprises a main body 502 having a cylindrical chamber 503a inside, a detective core 505 slidably fitted in the cylindrical chamber 503a, a spool 538 acting conjoinedly with the detective core 505 and designed to control the channel between an inlet port 532 and an outlet port 533, inflow passageways 517 bored in the main body 502 for leading flowing fluid into the detective core 505, and outflow passageways 513 bored in the detective core 505 for leading the flowing fluid brought in by the inflow passageways 517 to the main body 502, at least either the inflow passageways 517 or the outflow passageways 513 forming a certain angle of inclination with the axis of the detective core 505; the means for setting the mass flow rate 561 is designed to apply a set force to the detective core 505 and actuate the spool 538 so as to counterbalance the set force with a force produced by a change in momentum of the flowing fluid and acting on the detective core 505. The pressure line 585 extended from the variable displacement pump 571 is connected to the inflow passageways 517 at the flow detective unit 501 and also to the inlet port 532 by a pilot line 588, whereas the outlet port 533 is connected to the discharge control unit 572 by a line 591.
Flowing fluid supplied to the main body of the flow detective unit 501 is led at a certain inflow angle by the inflow passageways 517 in the main body into the detective core 505, then turned in its direction in the detective core 505, and led at a certain outflow angle by the outflow passageways 513 in the detective core 505 into the main body. Then, a change in momentum of the flowing fluid applies a force proportional to the mass flow to the detective core 505. The spool 538, joined with the detective core 505, is thereby moved to a position where the force proportional to the mass flow balances the force applied by the means for setting the mass flow rate 561 and thus controls the channel between the inlet port 532 and the outlet port 533. The opening of the channel between the discharge control unit 572 of the variable displacement pump 571 and the pressure line 585 or a tank 592 that results from the above-mentioned movement of the spool 538 actuates the discharge control unit 572 in its function to variably control the discharge rate of the variable displacement pump 571. Thus, on the basis of the mass flow, the discharge rate of the variable displacement pump 571 can be controlled in accordance with a prescribed rate with accuracy even where cavitation, bubbling, or the like occurs in the flow.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.